1. Field of the Invention
The present invention relates to an optical recording media capable of thermal sensitive recording by the scanning lights from a recording light source and process for producing the same.
2. Prior art of the Invention
Thermal sensitive recording is a direct recording method requiring developing and fixing.
This conventional method have been used in a simple terminal device of printer and facsimile since it can be easily operated and does not required much maintenance. However, in such a termal sensitive recording method, a thermal head or a thermal pen directly contacts a surface of the recording medium. As a result, dregs of the recording material adhere to the head or the pen. This adversely affects resolution and sensitivity of the the recording medium.
To overcome this difficulty, there has been proposed another conventional recording method in which a xenon lamp as a light source is exposured to color a thermal sensitive recording medium. Usual optical, thermal sensitive recording medium is provided to form a coloring agent on a substrate.
A recording original copy for transcription is laid on the medium and flashed by light from the light source. Then, the flashing light is absorbed into black portions of the copy to produce heat, and produced heat heats the coloring agent layer to produce the coloration in the recording medium. However, in this recording medium in this method, a considerable heat diffusion occurs at the black portions of the copy so that the medium is subjected to fogging and clouding around the recording image thereon, thereby lowering resolving power and sensitivity.
Instead of placing the copy on the recording medium in above-mentioned method, there has been proposed a recording method in which a coloring matter capable of absorbing wave length light of exposed light is dispersed into a thermal sensitive coloring agent so that the recording is effected by converting ther light absorbed in the coloring matter to heat.
In this case, however, the coloring matter such as Methylene Blue and Rhodamine B absorbs a visible light and in colored before the recording in effected. Therefore, the recording medium have a inferior contrast between before and after the recording. Also, there has been proposed an optical recording medium which contains near infrared light absorbing coloring matter as a light absorber dispersed into a thermal sensitive coloring agent. In this case, the medium has a week absorption in visible light region, and therefore this medium improves a contrast in the recording medium. With this method, however, it is unavoidable to lower a resolution of the medium due to fogging and clouding, and an uniform color development can not be obtained since the coloring material can not be uniformly dispersed in the coloring agent.
Conventional thermal sensitive medium is prepared by dispersing ununiformly the coloring agent and the developer into a binder in the form of colloid or microcapsule. Since recording parts in the thermal sensitive medium become white and opaque, high energy of recording light source have larger loss due to the scattering of the light in the direction of the thickness of the coloring agent layer, and therefore the recording medium has a lowered resolution and an inferior sensitivity.
The prior art optical recording materials with thermal coloration and conventional multi-coloring material will be described, U.S. Pat. No. 4,284,696 (Ishida et al.) discloses a light transmission particle containing as a colorless sublimable dye, an acyl leucophenoxazine compound to form a color image. This particle can produce a clear color image having little fogging and having an excellent resolving power.
Also, U.S. Pat. No. 4,311,750 (Kubo et al.) discloses a multi-color thermo-sensitive recording material comprising two thermo-sensitive coloring layers capable of forming different color respectively at different temperature. A discoloring layer comprising a cross-linking type resin is disposed between the two thermo-sensitive coloring layers. This discoloring layer is cross linked in the course of the coating of the thermo-sensitive layers, so as to prevent either of the two thermo-sensitive coloring layers from being dissolved.
However, the above-mentioned patents fail to solve fundamental problems encountered in the use of thermo-sensitive coloring material for optical recording. It is preferred that the optical recording medium comprises laminated coloring agent layer, light absorber layer and developer layer each having a uniform thickness in a direction perpendicular to the surface of the recording medium, these layers being separated from one another in the direction of the thickness of in the medium. It is desirable that the layer have such a transparency that it is allows the recording light to reach the light absorber layer without any loss.
Based on these thoughts, there has been proposed an optical recording medium of a multi-layer construction which is prepared by dissolving homogeneously a coloring agent, a developer and a light absorber in a polymer to form solutions and then spin coating these homogeneous solutions successively on a substrate to form the multi-layer. However, this method is disadvantageous in that each of the already coated intermediate layers is liable to be affected during the spin coating.
Also, the coloring agent and developer are diluted by the polymer solution so that the concentration of each homogeneous solution becomes lower. In the case where the coloring agent and the developer are added to the polymer in larger amount to increase the concentrations, it is difficult to a homogeneous solution. The resulting layer becomes turbid. The problems described above for the dispersion binder type medium are also encountered in this method.